The invention relates to a device for cutting plants.
A device for cutting plants in accordance with EP 351 989 is already known, wherein after a stop the adjustment of the line length of the cutting line is controlled during the restart by means of a slide which can be displaced by centrifugal force and has cams. When the device or the motor is stopped, the cam or the slide is returned into the unlocked initial position by spring means. When being restarted, the reel, which is taken along inside the rotating cup, can turn in relation to it sufficiently far so that a detent on the reel comes to rest against the cam and terminates the rotation by this.
The known device operates dependably, but consists of comparatively many individual parts and, in case of wear on the cutting line or loss of the cutting line, requires the stopping and restarting of the device for adjusting the cutting line. Automatic adjustment of the lost length of line is impossible during operation.
A corresponding device for cutting plants is also known from U.S. Pat. No. 4,347,666. Here a slide which can be displaced transversely to the axis of rotation and has a cam, releases detents on the reel or stops them. The line adjustment is controlled with this during the cutting of plants. The centrifugal force-controlled slide is maintained in its locked original position by a spring, wherein the line adjustment only operates if the cutting line operates, i.e. cuts plants. The line adjustment does not function if the line rotates in the air without hitting material to be cut. If in the course of wearing the free end of the line falls below a defined critical length, i.e. when the line cannot reach any more material to be cut, the automatic line adjustment does not function. The device must be shut off so that the line adjustment can be performed manually.
A further device for cutting plants is known from U.S. Pat. No. 4,104,796, wherein two spring-supported cams, which can be displaced by centrifugal force, unlock or lock at least one detent on the reel. This results in an rpm-dependent automatic adjustment of the cutting line. Because of the springs, this device is constructed comparatively elaborately. The springs must be calibrated exactly and the actual mass must exactly correspond to the calculated mass of each cam support. Even small spring force deviations and mass differences can change the control characteristic of the line adjustment in such a way that it does not respond inside the predetermined rpm range. In addition, such mass-spring systems are extremely trouble-prone. Even small amounts of dust, moisture or heat can lead to the failure or too early triggering of the line adjustment device. Therefore these springs need to be cleaned and adjusted often.
Further than that, the spring characteristic of the springs changes as a function of the rpm because of the centrifugal forces acting on the springs. The springs can furthermore interferingly act on the centrifugal force displacement because of their own mass.